Process and components for controlling the connections of a transmission system

ABSTRACT

A method is proposed for supervising the connections of a transmission system, said method establishing a logical connection between two components, such that one component in each case assumes the functions of a main components.  
     The components for carrying out the method must have devices which allow hierarchical operation of the transmission system.

[0001] The invention is based on a method for supervising theconnections of a transmission system according to the species defined inthe independent claim, and on devices for carrying out the method asdefined in the independent claim.

[0002] For networked information systems, in particular in a motorvehicle, components such as, for example, navigation units, CD changers,or a telephone are utilized in addition to a control unit (for examplethe conventional car radio). In complex networked systems, there isgenerally a need to specify suitable methods for smooth communicationamong all components. The communication system is separate from theactual application, and possesses, for example, a structure according tothe ISO's OSI model.

[0003] European Patent 511 794 discloses a system in which onedesignated station (“master”) establishes and terminates the connectionto the other stations (“slaves”). Following its activation or after areset, the “master” uses a signal to request all the “slaves” toestablish the connection.

[0004] In “master-slave” systems, which are usually simple,communication between the “slaves” cannot occur directly but rather ispossible only via the “master.” This places a load 25 on the entire bussystem over which transmission is occurring, and requires largecalculation capacity on the part of the “master” for forwardingmessages.

SUMMARY OF THE INVENTION

[0005] The method according to the present invention having thecharacterizing features of the independent claim has, in contrast, theadvantage that a logical point-to-point connection between components ispossible with no need for the information to pass through a designatedstation. It is thereby possible for messages to be sent directly betweentwo components. Forwarding of messages via the “master”—as required, forexample, in a simple “master-slave” system for communication between two“slaves”—can be eliminated. Any component can initiate connectionestablishment. The definition of component functions is important notfor connection establishment, but rather for maintaining the connection.The definition must, however, be made for all components a priori.

[0006] In particular, according to the method further components caneasily be added to an existing system, even during operation.

[0007] The load placed on the transmission line by the networkmanagement system may be regarded as very small.

[0008] The features set forth in the dependent claims make possible anadvantageous development of and improvement to the method.

[0009] The definition of the components, which is made a priori, isimportant for maintaining the connection. If the initiative forconnection establishment comes from a component to which, by definition,the monitoring and termination function for that connection wasallocated, that component will advantageously continue to maintain theconnection.

[0010] The initiative for establishment of a connection can just aseasily come from a component to which, according to the definition, nomonitoring or termination functions for that connection are allocated.In that case the logical component takes over further maintenance of theconnection to which the functions for that connection are allocated.

[0011] Because of the hierarchical structure, it is possible to performa subdivision into multiple systems which each comprise a (connection)“master” with the (connection) “slaves” allocated to it. In thisconnection it is possible on the one hand to operate a subsystem of thiskind in “stand-alone” fashion, i.e. without all the other components. Itis possible on the other hand to implement largely autonomoussubnetworks which “coexist,” almost without mutual influence, in termsof overall data traffic and network management.

[0012] Advantageously, connection establishment is initialized bysending identifiers.

[0013] In order to maintain the logical connections, it is advantageousif cyclical telegrams are sent out. The sending of test telegrams isadvantageous as a way to check physical connections.

[0014] The component according to the present invention having thecharacterizing features of the independent claim has the advantage thatthe component has a program which allows it to act both as a secondarycomponent in one connection and as a main component in anotherconnection.

[0015] Advantageously, the configuration data of the system are storedin nonvolatile memories, so that the overall network can be establishedmore completely after a restart. The storage of configuration data canalso be used for error detection and localization.

[0016] The components have circuits which allow a reduction in theoperating state, for example into sleep mode. This operating state isattained if the cyclical telegram of the main component is absent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Exemplary embodiments of the invention are depicted in thedrawings and explained in more detail in the description below. In thedrawings:

[0018]FIG. 1 shows the logical and physical components of a transmissionsystem according to the present invention;

[0019]FIG. 2 shows possible logical connections in the transmissionsystem;

[0020]FIG. 3 shows a simple exemplary embodiment;

[0021]FIG. 4 shows a first time diagram for connection establishment;

[0022]FIG. 5 shows a second time diagram for connection establishment;

[0023]FIG. 6 shows a time diagram for a component reset; and

[0024]FIG. 7 shows an exemplary embodiment of a component.

DETAILED DESCRIPTION

[0025] According to FIG. 1, each station has in conceptual terms thephysical device (PD) 2, which is defined by exactly one physicalinterface to the network or bus 1 and contains one or more logicalcomponents (LC) 3. When communication is being established betweendifferent components of a transmission system, communication is firstestablished in the lower layers of the ISO model, i.e. the physicallayer, the data link layer, and the network layer, and the transportlayer thereabove. The method according to the present invention has todo with network-wide coordination of these layers. The basis forconnection establishment is a transmission system in which both directaddressing (1-to-1 communication) and broadcast addressing (1-to-Ncommunication) can be implemented, and in which all the components inthe network can in principle be connected in the same physical manner.These criteria are met, for example, by the Controller Area Network(CAN) defined by German Patent 35 06 118. This bus system is intendedfor control data and supervision data. Audio or video data can also betransmitted separately. The communication software relevant forconnection establishment must support a connection-oriented service(point-to-point connection) between the logical components. Utilizationof a transport protocol as defined in German Patent 41 31 133 issuitable here. In the method according to the present invention, thefunction of the logical components in a connection is defined on thebasis of an identification number which is sent between two or morecomponents in the header of the data telegram. Only logical components 3are addressable as mutually independent functional units. In contrast tothe utilization of the CAN bus hitherto known, point-to-pointconnections are created between components, in addition to the broadcastcharacteristics, by sending out identifiers.

[0026] In contrast to the known systems, in this concept the terms“master” and “slave” are not defined absolutely (with reference to astation or logical component). The definition of the terms “master” and“slave” refers to the point-to-point connections between two logicalcomponents, of which exactly one represents the “master” and the othersthe “slave” for that connection. Since this relationship can inprinciple be different for each of the existing point-to-pointconnections, the terms “connection master” and “connection slave” wouldin fact be more correct. It is thus entirely possible for one and thesame component to act in one connection as “master,” but in another as“slave.” The function, within a connection, of a logical component whichhas “master” properties is to monitor and indirectly terminate a logicalconnection.

[0027]FIG. 2 shows a logical star structure comprising individualpoint-to-point connections, which can be implemented essentially asoften as desired within a network. Main component 4 maintains logicalconnections to its secondary components 6. One of secondary components7, however, establishes a direct subsystem with other secondarycomponents 8 via connections 9. Component 7 is thus a main componentwith respect to 8, but a secondary component with respect to 4.

[0028] The manner in which the connection is established will be 1$--explained in more detail below using an example (FIG. 3) that isdeliberately kept simple. Each logical component is accommodated in itsown housing, so that for this example LC=PD.

[0029] The example concerns a simple system made up of a navigation unit10, a CD changer 11, and a display and operating element 12. Logicalcomponents NAV, CDC, and MAS are located in these physical devices. Inthis example, the user interface is implemented in the last-namedcomponent. The hierarchical network allows a clear separation betweencommunication and application. The communication “master” could thus beintegrated into a component which does not contain a direct userinterface. Component MAS is the system “master” which contains themonitoring and termination function with respect to overall operatingfunctionality. The components exist in logical connections 5, while theyare physically linked via bus 1.

[0030] Communication between the components is transacted via twopoint-to-point connections, each implemented via a bidirectionaltransport connection. Component MAS 12 represents the “master” for bothconnections, and NAV 10 and CDC 11 respectively the “slave.” Transportconnections 5 of this exemplary embodiment use the following Data LinkIdentifiers which are sent via the CAN bus:

[0031] MAS <-> NAV (point-to-point)

[0032] Transmission identifier MAS/Reception identifier NAV: 0x448

[0033] Transmission identifier NAV/Reception identifier MAS: 0x248

[0034] MAS <-> CDC (point-to-point)

[0035] Transmission identifier MAS/Reception identifier CDC: 0x408

[0036] Transmission identifier CDC/Reception identifier MAS: 0x208

[0037] Connection Watchdog (broadcasting)

[0038] Transmission identifier MAS/Reception identifier NAV and CDC:0x001

[0039] The codings are depicted in Tables 1 and 2.

[0040] Table 1 lists only the logical components used in the examples.In this exemplary embodiment, a total of 255 addresses are reserved forcomponents in the field of mobile communications. Provision is made fora subdivision into groups of similar or identical components (lastcolumn of the table). For “master” components, the identifier of theConnection Watchdog that is sent out is identical to the respectivelogical component number (LC number).

[0041] For the system described, the services for the “master” networkmanagement system are thus to be implemented in component MAS 12, andthe services for the “slave” network management system in components NAV10 and CDC 11, if the functions of the components were defined a priori.“Main connections” refer to connections between the “main master” andits “slaves,” and “subconnections” to those between “submasters” andtheir “slaves.”

[0042] The distinction between “master” and “slave” for a connectionresults in two variants of the network management system forestablishing a connection.

[0043] a) “Master” Network Management Services

[0044] A telegram (Connection Watchdog) starts being sent out via a busbroadcast channel following initialization of the “master” component;this is initiated, for example, by actuation of a button by the user.For each logical component which is a “slave” with respect to this“master,” this telegram is a trigger signal to establish a connection.The respective “slave” thus establishes its connection using the methodspecified by the transport protocol. The network remains activated aslong as the logical “master” component sends out telegrams. When thenetwork is powered down, the “master” stops sending out the ConnectionWatchdog, whereupon, after a specific time interval, all connected“slaves” consider the respective connection terminated (indirecttermination).

[0045] If necessary, the “master” application can monitor the status ofthe connection to the “slave” by way of a cyclical “Connection Test”telegram (an optional service that, in contrast to the ConnectionWatchdog, is connection-oriented). This is done by monitoring thereaction to the telegram sent out to the “slave.” For example, if thereis no acknowledgment by the “slave” within a specified time, theConnection Test telegram is repeated. After a certain number ofunsuccessful repetitions, the connection is considered terminated andthe “master” can, if applicable, take further actions.

[0046] The sequence over time is shown in FIG. 4. Components CDC 11 andNAV 10 have already been initialized internally and are ready forcommunication; other circumstances result in slightly modified timesequences.

[0047] t₀: At this point in time all components are ready tocommunicate; component MAS 12 sends its first Connection Watchdog (WD)telegram using identifier 001.

[0048] t₁: In reaction to the Connection Watchdog telegram, componentNAV 10 begins establishing a connection to MAS 12 by way of a ConnectionSetup (CS) telegram using identifier 248.

[0049] t₂: Component MAS 12 has received the CS telegram from NAV 10,and to confirm connection establishment sends a Connection Acknowledge(CA) telegram with identifier 448 to NAV 10. The transport connectionMAS <-> NAV is then ready to operate, i.e. all the services fortransmitting application data between these two components can be used.

[0050] t₃: As described under t1, here component CDC 11 reports to MASusing identifier 208.

[0051] t₄: Component MAS 12 confirms connection establishment to CDC 11via a CA telegram using identifier 408. The second connection is thusalso ready to operate, and the entire network is therefore completelyenabled for the communication of application data.

[0052] t₅: After the Watchdog Timer has expired (time t_(WD) after t₀),MAS once again sends out a Connection Watchdog telegram. Since all theconnections have already been set up, this time the “slave” componentsdo not begin establishing a connection.

[0053] b) “Slave” Network Management Services

[0054] When the Connection Watchdog is first received (i.e. theconnection has not yet been established), the “slave” performs aconnection establishment to the “master” (monitor service for theConnection Watchdog of the relevant “master”). In all other cases, thepurpose of the Connection Watchdog is timeout monitoring of theconnection to the “master.” In other words, if this telegram has beenabsent and if a certain period of time has elapsed, the “slave”considers the connection terminated. The connection can then bere-established if the Connection Watchdog is received again.

[0055] There additionally exists, for both the “master” and the “slave”application, the possibility of actively establishing a connection toits counterpart as required. This is done using the connectionestablishment services defined in the transport protocol, which do notdiffer in terms of “master” and “slave” functionality. For example, ifthe connection is established by a “slave” not because it received aConnection Watchdog telegram but as the result of an initiative by the“slave,” supervision of the connection is then handled by the “master,”by sending out the Connection Watchdog. FIG. 5 illustrates the case inwhich a secondary component (“connection slave”) wakes up the network:

[0056] t₀: At this point in time component NAV 10 begins to wake up thenetwork using a CS telegram. Because of the wake-up capabilities of thecommunication system, an initialization of components MAS 12 and CDC 11then takes place. After this initialization, it is possible to receivethe CS telegram.

[0057] t₁: Since there has so far been no acknowledgment of the CStelegram, the timer (TAC) that is now expiring prompts anothertransmission by component NAV 10.

[0058] t₂: Component MAS 12 confirms connection establishment to NAV 10.

[0059] t₃: The Connection Watchdog telegram is sent out, causing theremainder of the system to power up; the rest of the sequencecorresponds to case I.

[0060] In FIG. 6, a reinitialization (reset) is performed in thenetwork.

[0061] t₀: At this point in time the network is completely activated,i.e. all connections are set up.

[0062] t₁: Component CDC performs a reset, triggered e.g. by a voltagedip. Among the results of this is that the connection to component MASis interrupted.

[0063] t₃: Based on the first Connection Watchdog telegram received forcomponent CDC (after the reset) at t₂, it initiates the (repeat) reportto MAS.

[0064] t₄: Acknowledgment by MAS; connection is again active.

[0065] The time sequence is identical if what occurs at time t₁ is not areset but rather the addition of component CDC for the first time. Sincethe remainder of the system is already fully capable of communicating,it is possible with the mechanism just described to implement a“reporting-in” process for previously uninstalled “slave” componentsduring operation.

[0066] Network Power-down

[0067] Network power-down is initiated by “master” component MAS 12.Because of the Connection Watchdog have stopped being sent out, a timerruns practically simultaneously in the connected “slave” components NAV10 and CDC 11 to monitor the watchdog (T_(WDC)). All connections arethen deactivated, and data exchange over the network is no longerpossible. Given appropriate hardware prerequisites, it is still possibleto switch the individual components into a power-saving mode (sleepmode).

[0068] The core of the invention is the expansion of the rigid“master-slave” architecture into a hierarchical system having anydesired number of (logical) subnetworks. The specification of thesesubnetworks is a “linear figure” of the specification of the mainnetwork, i.e. no further services are needed in order to implement it.The main network and subnetworks possess a logical star structure which,in its smallest embodiment, represents a logical point-to-pointconnection. The hierarchical network management system allows thecommunication software to be neatly structured.

[0069] As soon as the Connection Watchdog is detected, the “slave”component creates the connection to the “master” and thus reports to itfor the first time. In the “master” component, this initial report isadvantageously detected by comparison with the permanently stored lastsystem configuration, and suitable actions are taken, for example userinstructions regarding the new functionality. The absence of apreviously installed “slave” component is detected by the “master” nolater than the next system restart, once again by comparing the currentsystem configuration to the stored one. The “master” can then reactappropriately, for example by omitting user menus.

[0070] Because of the wake-up mechanism of the shared physical layer,the only possibility is for all bus subscribers always to be“communication-active” simultaneously (the associated applications, onthe other hand, can of course be in a state of reduced powerconsumption).

[0071] All subsystems must share the channel capacity of the datalink/physical layer.

[0072] As a rule, the (main) “master” always maintains logicalconnections to all the connected components. Located hierarchicallybelow them are the subnetworks (then de facto possessing equal access),which are usually less extensive. This is not absolutely necessary,however, since the network management system can also be used for anydesired configurations, for example with quasi-equal-access logicalnetworks (several “masters” on one hierarchical level).

[0073] The bus load resulting from the network management system may beregarded as quite small, since when the network is in initializedoperation only the cyclical Connection Watchdog telegrams of the“master” or “submaster” components are necessary. The associatedinterrupt rate is equally low, i.e. only a slight additional load on thecalculating capacity of the connected components.

[0074]FIG. 2 shows an example of a more complex system, comprising amain component (“master”) 4, MAS with five connections (MC, mainconnections) 5, a coordinated main component 7 (component NAV) of thesubsystem with a further two connections (SC, subconnections) 9, twosecondary components CDC 6, GAT 6 (connections only to MAS), andsecondary components TMC 6, 8, TEL 6, 8 (connections both to MAS and toNAV).

[0075] In terms of network management, this system can initially bedescribed as a combination of two simple systems as shown in FIG. 3,i.e. all the processes described there are correspondingly applicable.The essential expansions as compared with the simple system result fromthe two “master” components in hierarchical relationship (NAV 7 is a“slave” with respect to MAS 4), and from the two “slave” components (TEL6, 8, TMC 6, 8), which have more than one “master.”

[0076] Consistent behavior in terms of powering the network up and downcan be achieved with a few additions to the defined rules.

[0077] In the example, the “master” with the highest hierarchical level(MAS) 4 is always responsible for powering up (sending out the firstConnection Watchdog), and for powering down (withdrawal of theConnection Watchdog and, if applicable, a further “shutdown” message to“submaster” NAV 10) the entire network. This means that first the mainnetwork is activated (connections to MAS 4), and then the subnetwork(connections to NAV 7). The same applies to powering down. The networkmanagement system described here also, however, allows operating statesin which “submaster” NAV 7 independently activates and deactivates itssubnetwork (e.g. for data exchange with component TEL 6, 8).

[0078] Secondary components which possess more than one main component(in this example, TEL 6, 8 and TMC 6, 8) must ensure that theirapplication is not switched into sleep mode until all the “masters” havestopped sending out the Connection Watchdog.

[0079] In FIG. 7, a component is connected to bus 1 via interface 15(protocol module) and the bus coupling with wake-up capability 16(transceiver). The component is monitored by a microprocessor 18 andpossesses a nonvolatile memory 17. A module 19 to determine the time-outcan additionally be installed in the component. To eliminate the needfor a separate wake-up line, each station should be equipped withsuitable bus hardware (e.g. special transceiver module) allowing it,when bus traffic is detected, to generate a wake-up signal for its owninitialization. A switch between sleep mode and full activity for acomponent can easily be achieved in this fashion. This is the mostelegant way to wake up a component, although switching lines withmultiple access (each component has a write authorization to that line),or similar methods, are also possible.

[0080] To support the network management system, at least the morecomplex devices (operating element, navigation system, etc.), butideally all the components, should be capable of storing data regardingthe most recent network configuration (components connected, active ordisrupted connections) in permanent fashion (i.e. in a nonvolatilememory 17 such as an EEPROM). TABLE 1 Logical LC Number LC NumberAbbreviation Component (hex) Group (hex) MAS “Master” Unit 01 01-07 CDCCompact Disc 08 08-0F Changer 10-17 TMC Traffic 1C 18-1F Message Channel20-27 28-2F 30-37 38-3F 40-47 NAV Navigation 48 48-4F Unit TEL Telephone50 50-57 58-5F 60-67 68-6F 70-77 78-7F 80-87 88-8F 90-97 98-9F AO-A7A8-AF B0-B7 B8-BF C0-C7 C8-CF D0-D7 D8-DF E0-EF E8-EF GAT Gateway FOF0-F7 F8-FF

[0081] TABLE 2 “Connec′tion “Master” CAN “Connetion “Slave CAN IDMaster” ID (hex) Slave” (hex) a) Main Connections MAS 408 CDC 208 MAS41C TMC 21C MAS 448 NAV 248 MAS 450 TEL 250 MAS 4F0 GAT 2F0 . . . . . .. . . b) Subconnections NAV 508 TMC 509 NAV 540 TEL 541 . . . . . . . .. . . .

1. A method for supervising the connections of a transmission system, inparticular for use in a motor vehicle, the system having a bidirectionaltransmission line (1) and at least two physical components (2) connectedto the transmission line, characterized in that the physical componentscontain at least one logical component (3), and addresses which definethe function of the logical components are allocated to the latter; afirst logical component (3) emits the request for connectionestablishment to at least a second logical component (3); and the secondlogical component (3) creates the logical connection to the firstcomponent, one of the logical components assuming a monitoring andtermination function for that connection.
 2. The method for supervisingthe connections of a transmission system as defined in claim 1,characterized in that the first logical component (3) assumes themonitoring and control function for that connection.
 3. The method forsupervising the connections of a transmission system as defined in claim1, characterized in that the second logical component (3) assumes themonitoring and termination function for that connection.
 4. The methodfor supervising the connections of a transmission system as defined inclaim 1 through 3, characterized in that initialization of thetransmission system is achieved via a logical component by sending atransmission identifier.
 5. The method for supervising the connectionsof a transmission system as defined in claim 1 through 4, characterizedin that each logical connection in the transmission system is maintainedby cyclically sending out telegrams in a connection.
 6. The method forsupervising the connections of a transmission system as defined in claim1 through 5, characterized in that the physical connections in thetransmission system are monitored by cyclically sending out testtelegrams.
 7. The method for supervising the connections of atransmission system as defined in claims 1 through 6, characterized inthat the transmission system is switched into a sleep mode if notelegrams occur on the transmission lines within a predefined time.
 8. Aphysical component for carrying out the method as defined in one ofclaims 1 through 7, having at least one logical component, having aninterface module (15) for connection to the connection line (1) betweenfurther components (2) and a microprocessor (18) arranged in the logicalunit, and a nonvolatile memory (17) connected to the microprocessor,characterized in that a file which dictates to the component for aspecific connection establishment whether the component performs themonitoring and termination function in that connection is stored in thememory.
 9. The component as defined in claim 8, characterized in thatcomponents (2) possess a nonvolatile memory (17) for configuration dataof the transmission system.
 10. The component as defined in claim 8 or9, characterized in that the component (2) is designed for performingmonitoring tasks for logical connections.
 11. The component as definedin claim 8 through 10, characterized in that the components (2) possessa device (19) for time monitoring of the cyclical telegrams which, inthe absence of the telegrams, switches the component into areduced-power operating state.
 12. The apparatus as defined in claim 1through 12, characterized in that the components can be switched betweenseveral operating states with reduced energy consumption.